1. Field of the Invention
This invention relates to a fuel pump assembly suitably used in a vehicle, and more particularly, to a fuel pump assembly in which discharge noise of vapor generated in fuel is reduced.
2. Description of the Prior Art
Referring to FIGS. 6 to 9, a conventional fuel pump assembly 2 will be described. The fuel pump assembly 2 shown in FIG. 6 and FIG. 7 representing, respectively, a sectional side view and a bottom end view, comprises a cylindrical metal housing 8, a motor section 10 disposed at an upper part of the housing 8, and a pump section 14 disposed at a lower part thereof. The motor section 10 and the pump section 14 are separated by an aluminum die-cast cover member 12. The fuel pump assembly 2 is mounted in a fuel tank (not shown) through a metal bracket 6 substantially in a vertical manner.
The motor section 10 is composed of an electric motor having a rotor 16 and a driving shaft 18. In the pump section 14, the driving shaft 18 is inserted through a hole formed in the central portion of the cover member 12. The driving shaft 18 has mounted thereon a first impeller 20 and a second impeller 22 rotatable in association with the driving shaft 18. The impellers 20 and 22 are made of synthetic resin each having a plurality of cutout portions or vanes (not numbered) along the outer periphery thereof. The cover member 12, an aluminum die-cast fixing plate 28, and a housing body 226 are fixed at the bottom part of the housing 8 by caulking the bottom end periphery thereof.
As should be apparent from the drawings, the cover member 12, the fixing plate 28, and the housing body 226 are integrally assembled to form a first pump chamber 42 and a second pump chamber 44 each having a substantially C-shaped section along the respective outer periphery of the impellers 20 and 22. The pump chambers 42 and 44 communicate with each other by a through hole (not shown) formed in the fixing plate 28. The second pump chamber 44 communicates with the interior of the housing 8 through an outlet port 246 formed in the cover member 12. On the other hand, the first pump chamber 42 communicates with the interior of a fuel tank through an inlet port 248 formed in the housing body 226. The inlet port 248 is connected to a fuel filter 31.
FIG. 8 is a bottom end view of the fuel pump assembly 2 with a part broken away, and FIG. 9 is a sectional side view of the housing body 226. The housing body 226 has a small vapor by-pass port 250 communicating with the first pump chamber 42. The vapor by-pass port 250 serves for discharging vapor from the fuel flow in the first pump chamber 42 to the outside thereof and this port is bored by drilling at a predetermined angle at a location apart from the inlet port 248.
The housing body 226 has a chamber 262 formed at the outlet side of the by-pass port 250. The chamber 262 is formed such that a recess 252 having a bore diameter larger than that of the vapor by-pass port 250 is drilled and then, a bottom opening of the recess 252 is covered by a metal or resin cover plate 253. The plate 253 is fitted by press-fitting or the like.
The housing body 226 has a small restriction 260 formed at a side surface of the chamber 262 by drilling or the like so as to radially pass through the wall of the chamber 262 (substantially perpendicular to the vapor by-pass port 250). Accordingly, the chamber 262 is opened to the interior of the fuel tank.
As shown in FIG. 6, the fuel pump assembly 2 is mounted on the bracket 6 with a rubber cushion material 54 inserted at the bottom of the housing body 226. The cushion material 54 prevents vibrations of the fuel pump assembly 2 from being transmitted to the bracket 6.
The effects of the fuel pump assembly thus constructed will now be described. When the motor section 10 is driven to rotate the impellers 20 and 22, the fuel is increased in pressure in the first pump chamber 42, and is introduced into the second pump chamber 44 through the through hole formed in the fixing plate 28. The fuel is further increased in pressure in the second pump chamber 44.
Under the two-step pressure increasing action attained by the rotations of the impellers 20 and 22, the fuel is sucked from the inlet port 248 and is pumped from the outlet port 246 into the housing 8 passing through both the pump chambers 42 and 44. The fuel thus pumped into the housing 8 is further fed forcedly to an engine (not shown).
In this conventional pump, the vapor generated by temperature rise in the fuel tank and by the above-described fuel sucking effect is discharged, as a vapor-mixed fuel, from the pump chamber 42 through the vapor by-pass port 250 of the housing body 226 into the chamber 262, and is then discharged into the fuel tank through the restriction 260. With this construction, the vapor content rate in the fuel fed from the housing 8 to the engine is naturally reduced, thus preventing a vapor-lock of the engine or the fuel pump.
The above-described fuel pump assembly 2 is disclosed, for example, in Japanese Utility Model Publication No. 6-14073 proposed by the same assignee as the present invention. The provision of the fuel pump assembly 2 in the fuel tank is disclosed in the Japanese Utility Model Publication No. 6-14073, and its description will not be repeated.
In the fuel pump assembly 2 thus constructed, discharge noise caused by the vapor-mixed fuel passing through the vapor by-pass port 250 is reduced to some degree by the chamber 262.
However, the shape of the chamber 262 is so simple that the reduction of the discharge noise is not enough. Furthermore, the area of the restriction 260 must be small in order to efficiently keep the noise reduction effect brought about by the chamber 262, thus prohibiting the gentle discharge speed of the vapor-mixed fuel from the restriction 260. Therefore, noise and vibrations are also generated when the energetically released vapor-mixed fuel impinges the bracket 6 or a wall surface of a subtank accommodating the fuel pump assembly 2 and the fuel filter 31.